Wiring a VegTherm into the tank selector switch on a 1984 F-250 IDI

[mankypro]

Have you done this? I want my vegtherm mega only to be on when my WO tank is selected - the rear position. I was hoping to wire into my oem selector switch.

If anyone has any information on how to accomplish this your input would be greatly appreciated.

[leongriffin]

The details will depend on how your tank selector work but in simple terms; You will use the output of the selector switch to trigger a relay that will turn your vegtherm on.

Get a 5 pin (SPDT) automotive relay and add it after the switch. (Pin 85 and 86) Out put from switch goes through the relay.

Wire power for the vegtherm (fused) to the relay Pin 30 and out either the NO Pin 87 (Normaly Open) or NC Pin 87A (Normaly Closed) depending on your selector.

Leon
WVOdesigns.com

[mankypro]

Please check -

Ok, so on the standard Bosch relay:

pin 30 goes to the battery +
pin 85 goes to the battery -
pin 86 goes to the tank switch - which will energize the relay allowing power to the vegtherm
pin 87 goes to the vegtherm +

Do I have that right?

I guess my biggest question is the tank switch and it's operation as it relates to the valve - the reason I'd like to know this is that knowing how it's wired (e.g. rear tank on when open, front when closed) will help me with wiring.

[leongriffin]

Nope, not even close! Not to fear, this sparky stuff is not really that hard.

OK, take a step back and look at what a relay is and what you want to do:

Think of a relay as an "IF THEN" ie. IF the tank selector is engaged, THEN engaged the heater. when current is flowing through the IF the relay flips an internal switch for another totally independent circuit. Typically this is used so that you can use a low current source to engage a high current application.

As far as wiring, you first add the relay to the "IF" circuit: there will be a wire leaving the selector switch that goes "ON" and "OFF" with the switch; cut that wire and connect one end to 85 and one to 86. The current will flow through the relay uninteruped and activate the tank selector valve as it did before. You now have an active relay switch; connect a +12V source to pin 30, if you connect directly to the battery, get a 30A breaker and install that close to the battery, trust me on this. If you don't already have a $5 tester light; get one, you need to be able to see what is HOT and what is not. Connect EITHER 87 or 87A to the heater + and ground the heater -. You could just guess and it will either be correct or backwards (on when you want it off and off when you want it one).

Google "how a relay works" , take a look at the schematic that comes with the relay and play around with it a bit. You will have a clear understanding of it by the time you are finished.

Leon
WVOdesigns

[mankypro]

Leon,

Thanks for the mini-tutorial. So the tank selector switch on my dash (oem) is on or off? That is current is being supplied or not? That's the way the valve works?

Just wondering, I guess I'll find out with me test light...

Originally Posted by leongriffin

Nope, not even close! Not to fear, this sparky stuff is not really that hard.

OK, take a step back and look at what a relay is and what you want to do:

Think of a relay as an "IF THEN" ie. IF the tank selector is engaged, THEN engaged the heater. when current is flowing through the IF the relay flips an internal switch for another totally independent circuit. Typically this is used so that you can use a low current source to engage a high current application.

As far as wiring, you first add the relay to the "IF" circuit: there will be a wire leaving the selector switch that goes "ON" and "OFF" with the switch; cut that wire and connect one end to 85 and one to 86. The current will flow through the relay uninteruped and activate the tank selector valve as it did before. You now have an active relay switch; connect a +12V source to pin 30, if you connect directly to the battery, get a 30A breaker and install that close to the battery, trust me on this. If you don't already have a $5 tester light; get one, you need to be able to see what is HOT and what is not. Connect EITHER 87 or 87A to the heater + and ground the heater -. You could just guess and it will either be correct or backwards (on when you want it off and off when you want it one).

Google "how a relay works" , take a look at the schematic that comes with the relay and play around with it a bit. You will have a clear understanding of it by the time you are finished.

Leon
WVOdesigns

[leongriffin]

Yes, a little time with a test light under the dash will make everything much more clear.

Leon
WVOdesigns.com

[hheynow]

Originally Posted by mankypro

Have you done this? I want my vegtherm mega only to be on when my WO tank is selected - the rear position. I was hoping to wire into my oem selector switch.

If anyone has any information on how to accomplish this your input would be greatly appreciated.

The fuel tank selector valve inside your frame rail has connector wires. Find the terminal that's hot when on your WMO tank. Connect this terminal to the 85 of your relay. That way the vegtherm only gets power when on WMO tank. A test light should be all you need. Study these links.
The Bosch Relay Unraveled
Fog Light Wiring with Bosch Relay

[mankypro]

Thank you.

I've heard scurrilous rumors about the switch in my truck and the tank selector switch not being energized but momentarily during the switchover. Any credence to this?

1984 f-250 4x4 scab 6.9l IHC

Originally Posted by hheynow

The fuel tank selector valve inside your frame rail has connector wires. Find the terminal that's hot when on your WMO tank. Connect this terminal to the 85 of your relay. That way the vegtherm only gets power when on WMO tank. A test light should be all you need. Study these links.
The Bosch Relay Unraveled
Fog Light Wiring with Bosch Relay

[hheynow]

The only momentary lapse is between your ears.
Sorry dude couldn't help myself.

[mankypro]

Originally Posted by hheynow

The only momentary lapse is between your ears.
Sorry dude couldn't help myself.

[mankypro]

Ok this is silly there are 8 freaking different wires going into my tank valve. With my luck I'll find the wire after I snip all 8 wires.

It's silly that there isn't a diagram somewhere with wire colors...

[hheynow]

Don't cut them yet. Use a cheepo test light, the kind with the sharp point and alligator clip. Stab each wire until you see which one is hot while on the WMO tank.